<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        input {
            color: #999;
        }
    </style>
</head>

<body>
    <input type="text" value="手机">

    <script>
        //1.获取元素
        var text = document.querySelector('input');

        //2.绑定事件   onfocus 获得焦点
        text.onfocus = function () {
            // console.log('获得焦点');
            if (this.value == '手机') {
                this.value = '';
            }
            this.style.color = '#333';
        }

        //当我们失去焦点  onblur
        text.onblur = function () {
            // console.log('失去焦点');
            if (this.value == '') {
                this.value = '手机';
            }
            this.style.color = '#999';
        }
    </script>
</body>

</html>